This disclosure is generally directed to imaging members, devices, photoreceptors, photoconductors, and the like. More specifically, the present disclosure is directed to rigid or multilayered flexible, belt imaging members, or devices comprised of a supporting medium like a substrate, and which photoconductor contains a fluoroalkyl ester anticurl back coating (ACBC), and more specifically, a layer of a fluoroalkyl ester situated on the reverse side of the photoconductor substrate; a photogenerating layer; an optional undercoat or hole blocking layer usually situated between the substrate and the photogenerating layer, and at least one charge transport layer, wherein at least one is from 1 to about 5, from 1 to about 3, 2, one, and the like, such as a first charge transport layer, and a second charge transport layer, a hole blocking layer, an optional adhesive layer, and an optional overcoating layer, and wherein at least one of the charge transport layers contains at least one charge transport component, and a polymer or resin binder, and where in embodiments the resin binder selected for the hole blocking layer is a known suitable binder including a binder that is substantially insoluble in a number of solvents like methylene chloride, examples of these binders being illustrated in copending application U.S. application Ser. No. 11/593,658, the disclosure of which is totally incorporated herein by reference. Also, in embodiments the present disclosure is directed to photoconductors where a fluoroalkyl ester is incorporated into at least one of the charge transport layers or into an optional overcoating layer and where in embodiments the overcoating layer is free of the ester.
For flexible photoconductive members, to offset undesirable curling thereof, an anticurl back coating is applied to the backside of the flexible substrate support, opposite to the side of the photogenerating layer, that is the anticurl layer is in contact with the reverse side of the substrate resulting in a substantially flat photoconductor member web. Curling of a photoreceptor web is undesirable because, for example, it hinders fabrication of the web into cut sheets and subsequent welding into a belt. An anticurl back coating having a counter curling effect equal to and in the opposite direction to the applied layers is deposited on the reverse side of the active imaging member substrate to eliminate or minimize the overall curl of the coated member by offsetting the curl effect which arises from the mismatch of the thermal contraction coefficient between the substrate and the charge transport layer resulting in greater charge transport layer dimensional shrinkage than that of the substrate.
Although an anticurl back coating is selected to counteract and balance the curl so as to allow the imaging member web to lay flat, nonetheless, common formulations used for anticurl back coatings have in a number of instances been found to provide unsatisfying dynamic imaging member belt performance under normal machine functioning conditions; for example, exhibition of excessive anticurl back coating wear and its propensity to cause electrostatic charge buildup are the frequently seen problems that prematurely reduce the service life of the photoreceptor belt and require its frequent costly replacement in the field.
Moreover, high surface contact friction of the anticurl back coating against all these machine subsystems can cause the development of electrostatic charge buildups. In a number of xerographic machines, the electrostatic charge builds up due to the high contact friction between the anticurl back coating and the backer bars which increases the frictional force to the point that it requires higher torque from the driving motor to pull the belt for effective cycling motion. In full color electrophotographic machines using a 10-pitch photoreceptor belt, the electrostatic charge build-up can be extremely high due to the large number of backer bars used in the machine.
In an effort to resolve the problems associated with a number of anticurl back coatings, one known wear resistance anticurl back coating formulated for use in the printing apparatuses includes organic reinforcement particles such as a polytetrafluoroethylene (PTFE) dispersion contained in the anticurl back coating polymer binder. PTFE particles are commonly incorporated to reduce the friction between the anticurl back coating of the belt and the backer bars. The benefit of using this formulation may, however, be outweighed by the instability of the PTFE particle dispersion in the anticurl back coating solution. PTFE, being two times heavier than most coating solutions selected, forms an unstable dispersion in a polymer coating solution, commonly a bisphenol A polycarbonate polymer solution, and tends to settle where particles flocculate themselves into large agglomerates in the mix tanks if not continuously stirred. The difficulty of achieving good PTFE dispersion in a coating solution can be a problem since inorganic dispersion can result in an anticurl back coating with insufficient and variable or inhomogeneous dispersions along the length of the coated web, and thus, a substantially inadequate reduction of friction over the backer bars contained in a copier or printer. This can cause complications for larger copiers or printers, which often include many backer bars, where the high friction increases the torque needed to drive the belt. Consequently, two driving rollers are included and synchronized to substantially prevent any registration error from occurring. The additional components, such as the two driving rollers result in high costs for producing and using these larger printing apparatuses. Thus, if the friction could be reduced, the apparatus design in these larger printing apparatuses could be simplified with less components resulting in a substantial cost savings.
Examples of anticurl back coating formulations are disclosed in U.S. Pat. Nos. 5,069,993; 5,021,309; 5,919,590; 4,654,284 and 6,528,226. However, while these formulations serve their intended purposes, further improvement on those formulations is desirable and needed. More particularly, there is a need, which is addressed herein, to create an anticurl back coating formulation that has intrinsic properties to minimize or eliminate charge accumulation in photoreceptors without sacrificing the other electrical properties such as low surface energy.
Photoconductors containing fluorinated polymers, such as polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE), in the ACBC layer can be difficult to prepare, and uniform and stable dispersions thereof usually cannot be obtained; the ACBC layer containing a fluoropolymer tends to charge up triboelectrically due to the rubbing of this layer against, for example, backer plates and rollers in, for example, a printing machine, resulting in electrostatic drag force that adversely affects the process speed of a photoconductor present in the machine; fluoropolymer particles or debris adversely affect other related systems in the machine; and there can be charge accumulation on the ACBC surface resulting from, for example, the bulk conductivity of the ACBC. Low surface energy charge transport layers are desirable for photoconductors to permit excellent wear resistance characteristics, emulsion aggregation toner cleanability, and anti-filming properties, all of which are not readily achievable with the incorporation of fluoropolymers in the charge transport layer. Also, for flexible belt photoconductors is the unwanted LCM that is generated from fluoropolymer (PTFE/surfactant dopants) since unlike in drum P/R, the charge transport layer degrades or wears from blade cleaning in belt photoconductors, thus conductive species tend to accumulate on the surface resulting in LCM. These and other disadvantages are avoided or minimized with the photoconductors of the present disclosure that contain a fluoroalkyl ester in the ACBC and/or the charge transport layer or optional overcoating layer.
Also included within the scope of the present disclosure are methods of imaging and printing with the photoconductors illustrated herein. These methods generally involve the formation of an electrostatic latent image on the imaging member, followed by developing the image with a toner composition comprised, for example, of thermoplastic resin, colorant, such as pigment, charge additive, and surface additive, reference U.S. Pat. Nos. 4,560,635; 4,298,697 and 4,338,390, the disclosures of which are totally incorporated herein by reference, subsequently transferring the image to a suitable substrate, and permanently affixing the image thereto. In those environments wherein the photoconductor is to be used in a printing mode, the imaging method involves the same operation with the exception that exposure can be accomplished with a laser device or image bar. More specifically, the flexible photoconductor belts disclosed herein can be selected for the Xerox Corporation iGEN® machines that generate with some versions over 100 copies per minute. Processes of imaging, especially xerographic imaging and printing, including digital, and/or color printing, are thus encompassed by the present disclosure.
The photoreceptors illustrated herein, in embodiments, have extended lifetimes; possess excellent, and in a number of instances low Vr (residual potential); and allow the substantial prevention of Vr cycle up when appropriate; high sensitivity; low acceptable image ghosting characteristics; and desirable toner cleanability.